path: root/drivers/md/dm-snap.c

/*
 * dm-snapshot.c
 *
 * Copyright (C) 2001-2002 Sistina Software (UK) Limited.
 *
 * This file is released under the GPL.
 */

#include <linux/blkdev.h>
#include <linux/ctype.h>
#include <linux/device-mapper.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/kdev_t.h>
#include <linux/list.h>
#include <linux/mempool.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/log2.h>
#include <linux/dm-kcopyd.h>

#include "dm-snap.h"
#include "dm-bio-list.h"

#define DM_MSG_PREFIX "snapshots"

/*
 * The percentage increment we will wake up users at
 */
#define WAKE_UP_PERCENT 5

/*
 * kcopyd priority of snapshot operations
 */
#define SNAPSHOT_COPY_PRIORITY 2

/*
 * Reserve 1MB for each snapshot initially (with minimum of 1 page).
 */
#define SNAPSHOT_PAGES (((1UL << 20) >> PAGE_SHIFT) ? : 1)

/*
 * The size of the mempool used to track chunks in use.
 */
#define MIN_IOS 256

static struct workqueue_struct *ksnapd;
static void flush_queued_bios(struct work_struct *work);

struct dm_snap_pending_exception {
	struct dm_snap_exception e;

	/*
	 * Origin buffers waiting for this to complete are held
	 * in a bio list
	 */
	struct bio_list origin_bios;
	struct bio_list snapshot_bios;

	/*
	 * Short-term queue of pending exceptions prior to submission.
	 */
	struct list_head list;

	/*
	 * The primary pending_exception is the one that holds
	 * the ref_count and the list of origin_bios for a
	 * group of pending_exceptions.  It is always last to get freed.
	 * These fields get set up when writing to the origin.
	 */
	struct dm_snap_pending_exception *primary_pe;

	/*
	 * Number of pending_exceptions processing this chunk.
	 * When this drops to zero we must complete the origin bios.
	 * If incrementing or decrementing this, hold pe->snap->lock for
	 * the sibling concerned and not pe->primary_pe->snap->lock unless
	 * they are the same.
	 */
	atomic_t ref_count;

	/* Pointer back to snapshot context */
	struct dm_snapshot *snap;

	/*
	 * 1 indicates the exception has already been sent to
	 * kcopyd.
	 */
	int started